The present invention relates to the field of geophones for collecting seismic data. More particularly, the invention relates to an improved apparatus and method for attaching geophones to soil.
Seismic exploration techniques examine subsurface geologic formations by sending a signal into the geologic formations and by sensing seismic waves reflected from the geologic formations. The seismic waves are detected with geophones connected by a leader wire to create a geophone string. Each geophone generates signals transmitted to a recording station through conductors in the leader wire or through wireless transmission techniques. The signals and positions of each geophone are processed to generate profiles of the subsurface geologic formations.
In marine seismic operations, geophone strings are towed behind a seismic vessel to record signals reflected from the subsurface geologic formations or are positioned as bottom cables on the soil underlying the water. Onshore, geophone strings are positioned in an array on the soil surface to record the reflected signals. As used herein, the term "soil" can comprise a variety of materials including dirt, sand, hardpan, rock, or submerged sediments.
One approach uses specialized tools to place geophones in the soil. U.S. Pat. No. 4,838,379 to Maxwell (1989) disclosed a tool for orienting a geophone in a selected direction. U.S. Pat. No. 5,007,031 to Erich (1991) disclosed a planting tool for placing a geophone in a shallow hole.
Other approaches emphasize the connection between a geophone case and the seismic cable. U.S. Pat. No. 3,931,453 to Hall (1976) disclosed a geophone case attached to a seismic cable wherein the cable was run through two 180 degree bends to strengthen the connection between the case and cable. U.S. Pat. No. 4,470,134 to McNeel (1984) disclosed a geophone case attached to a cable with inner and outer connections.
Certain geophone designs have spikes attached to a geophone case for providing engagement with soil. A representative example of a land based geophone is described in U.S. Pat. No. 5,010,531 to McNeel which showed ground coupling spikes attached to the geophone for stabilizing the geophone and for improving the contact between the geophone and the ground. These ground coupling spikes were installed by workers during the placement of the geophone strings and reduced instability of unanchored geophones. U.S. Pat. No. 5,124,956 to Rice et al. (1992) disclosed a geophone case having spikes with weighted tips and larger diameter bow springs. U.S. Pat. No. 5,130,954 to Fussell (1992) disclosed a geophone case having a spike on the case lower end for penetrating the soil.
Other systems have focused on retrieving seismic geophones after the geophones have been installed on the soil underlying water. U.S. Pat. No. 5,189,642 to Donoho (1993) disclosed an elaborate system for using a buoy to retrieve a geophone. U.S. Pat. No. 5,978,317 to Whitener (1999) disclosed a system for burying geophones in storage containers and for recovering such geophones at a later date.
Ocean bottom systems rely upon the weight of the geophones and cable to couple the geophones with to the soil. Gravity coupling of the geophones in certain marine environments does not provide good data quality.
Minaturization of geophone components has reduced geophone sizes and sometimes permits the integration of geophones into the geophone strings. Techniques for fixing the location of such geophones has not been developed, and is needed to prevent geophone movement after the location of each geophone is established. Accordingly, a need exists for an improved system for anchoring geophones to soil.